Exchange-traded funds offer a convenient way to invest in sectors or niches that interest you. If you expect the global agriculture industry to thrive as the world's population grows, the PowerShares Global Agriculture ETF (NYSE: PAGG) could save you a lot of trouble. Instead of trying to figure out which companies will perform best, you can use this ETF to invest in lots of them simultaneously.

The basics
ETFs often sport lower expense ratios than their mutual fund cousins. This ETF's expense ratio -- its annual fee -- is 0.75%, which is pretty high for an ETF but is still less than the typical stock mutual fund.

This ETF has performed reasonably well, but it's also very young, with just two full (and market-beating) years on the books. As with most investments, of course, we can't expect outstanding performances in every quarter or year. Investors with conviction need to wait for their holdings to deliver.

With a low turnover rate of 19%, this fund isn't frantically and frequently rejiggering its holdings, as many funds do.

What's in it?
Several of this ETF's components made strong contributions to its performance over the past year. Seed and herbicide king Monsanto (NYSE: MON) and fertilizer giant Mosaic (NYSE: MOS), up about 19% and 18% respectively over the past year, stand to benefit from rising food prices. They might also get a boost from the increasing value of farmland, which has been linked to rising inflation. PotashCorp (NYSE: POT) gained roughly 15%. It's a giant in the field of fertilizer, a sector many expect robust growth from in the years ahead.

Some smaller companies such as Agrium (NYSE: AGU) may grow even faster. Agrium has been posting strong growth, and though it's taken on more debt to fuel acquisitions, its cash flow easily covers those obligations.

Other companies didn't add as much to the ETF's returns last year, but could have an effect in the years to come. American crop titan Archer Daniels Midland (NYSE: ADM), down about 7% over the past year, is profiting from surging demand for corn for ethanol and other purposes, and plans to expand in the Black Sea region.

The big picture
Demand for agriculture is likely to remain as long as humans inhabit the earth. A well-chosen ETF can grant you instant diversification across any industry or group of companies -- and make investing in and profiting from it that much easier.

ETFs can help you find the way to better investing results. To find some great ETF investing ideas, take a look at The Motley Fool's special free report, " 3 ETFs Set to Soar During the Recovery ."

Longtime Fool contributor Selena Maranjian holds no position in any company mentioned. Click here to see her holdings and a short bio. Motley Fool newsletter services have recommended creating a synthetic long position in Monsanto. Try any of our Foolish newsletter services free for 30 days. We Fools may not all hold the same opinions, but we all believe that considering a diverse range of insights makes us better investors. The Motley Fool has a disclosure policy.